This invention relates to a device for separating impurities such as trash, shell fragments and the like from fiber material during its treatment by a carding machine or a roller card unit. The device is situated above the licker-in and has a knife blade which is oriented against the direction of rotation of the main carding cylinder and is at a small radial distance therefrom. A plate is held at a small radial distance from the main cylinder and at a small circumferential distance from the knife blade upstream thereof as viewed in the direction of rotation of the carding cylinder. The separating device further has a suction arrangement which includes a suction chamber extending over the clearance defined between the plate and the knife blade.
According to a known device, the knife blade is situated approximately in the middle between the licker-in and the frontal deflecting roller for the travelling flats. At that location, the cover of the cylinder has an opening. The air pressure generated by the rotation of the carding cylinder generates a strong air stream escaping through the opening. Such strong air stream is disadvantageous in that useful fibers are entrained thereby in large quantities.